[Audio Player] Cleanup the code along with closure compiler

ui/file_manager/audio_player/elements/control_panel.js

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function() {
   'use strict';
 
   /**
    * Moves |target| element above |anchor| element, in order to match the
    * bottom lines.
@@ skipping 16 matching lines @@
 
   /**
    * Converts the time into human friendly string.
    * @param {number} time Time to be converted.
    * @return {string} String representation of the given time
    */
   function time2string(time) {
     return ~~(time / 60000) + ':' + ('0' + ~~(time / 1000 % 60)).slice(-2);
   }
 
-  Polymer('control-panel', {
+  /**
+   * @constructor
+   * @extends {PolymerElement}
+   */
+  var ControlPanelElement = function() {};
+
+  ControlPanelElement.prototype = {
     /**
      * Initializes an element. This method is called automatically when the
      * element is ready.
      */
     ready: function() {
       var onFocusoutBound = this.onVolumeControllerFocusout_.bind(this);
-      this.$.volumeSlider.addEventListener('focusout', onFocusoutBound);
-      this.$.volumeButton.addEventListener('focusout', onFocusoutBound);
+
+      this.volumeSlider = this.$.volumeSlider;
+      this.volumeButton = this.$.volumeButton;
+      this.volumeContainer = this.$.volumeContainer;
+
+      this.volumeSlider.addEventListener('focusout', onFocusoutBound);
+      this.volumeButton.addEventListener('focusout', onFocusoutBound);
     },
 
     /**
      * Model object of the Audio Player.
      * @type {AudioPlayerModel}
      */
     model: null,
 
     /**
      * Invoked when the model changed.
      * @param {AudioPlayerModel} oldValue Old Value.
      * @param {AudioPlayerModel} newValue New Value.
      */
     modelChanged: function(oldValue, newValue) {
-      this.$.volumeSlider.model = newValue;
+      this.volumeSlider.model = newValue;
     },
 
     /**
      * Current elapsed time in the current music in millisecond.
      * @type {number}
      */
     time: 0,
 
     /**
      * String representation of 'time'.
@@ skipping 58 matching lines @@
 
     /**
      * Invoked when the previous button is clicked.
      */
     previousClick: function() {
       this.fire('previous-clicked');
     },
 
     /**
      * Invoked the volume button is clicked.
-     * @type {Event} event The event.
+     * @param {!Event} event The event.
      */
     volumeButtonClick: function(event) {
       this.showVolumeController_(this.volumeSliderShown);
       event.stopPropagation();
     },
 
     /**
      * Invoked when the focus goes out of the volume elements.
-     * @param {FocusEvent} event The focusout event.
+     * @param {!FocusEvent} event The focusout event.
      * @private
      */
     onVolumeControllerFocusout_: function(event) {
       if (this.volumeSliderShown) {
         // If the focus goes out of the volume, hide the volume control.
         if (!event.relatedTarget ||
-            (event.relatedTarget !== this.$.volumeButton &&
-             event.relatedTarget !== this.$.volumeSlider)) {
+            (event.relatedTarget !== this.volumeButton &&
+             event.relatedTarget !== this.volumeSlider)) {
           this.showVolumeController_(false);
           this.volumeSliderShown = false;
         }
       }
     },
 
     /**
      * Shows/hides the volume controller.
      * @param {boolean} show True to show the controller, false to hide.
      * @private
      */
     showVolumeController_: function(show) {
       if (show) {
         matchBottomLine(this.$.volumeContainer, this.$.volumeButton);
-        this.$.volumeContainer.style.visibility = 'visible';
+        this.volumeContainer.style.visibility = 'visible';
       } else {
-        this.$.volumeContainer.style.visibility = 'hidden';
+        this.volumeContainer.style.visibility = 'hidden';
       }
     },
-  });
+  };
+
+  Polymer('control-panel', ControlPanelElement.prototype);
 })();  // Anonymous closure